A driving device for a scanner includes an elongate guiding unit mounted in a base and disposed under an image sensor carriage that extends in a first direction, extending along a second direction transverse to the first direction, and having first and second side rail surfaces transverse to a top rail surface. A roller unit is mounted rotatably on a bottom side of the image sensor carriage, and includes a first roller rotatable about a first axis parallel to the first direction and disposed to roll along the top rail surface, and a second roller rotatable about a second axis transverse to the first and second directions and disposed to roll along the first side rail surface. A spring-loaded retaining unit is mounted on the image sensor carriage, and is disposed to contact rotatablely the second side rail surface. A driving unit drives the image sensor carriage to move in the second direction in the base.